CRT device implant can be challenging, for example, when the left ventricular (LV) lead is placed intravenously, advancing through the coronary sinus (CS) and into a selected branch of the cardiac venous system. It can be difficult to find an optimal location for placement of the lead due to patient variability in venous anatomy. A further challenge, after lead implant, is that positional changes may cause the lead to be micro-dislodged or even migrated. This may result in a decrease of the diaphragmatic stimulation threshold (i.e. the threshold above which a stimulation pulse delivered using the lead inadvertently triggers contraction of diaphragmatic muscles) and/or an increase of the LV capture threshold (i.e. a threshold above which a stimulation pulse properly triggers contraction of LV myocardial tissues.) LV pacing pulses should be set with a pulse magnitude above the LV capture threshold and yet below the diaphragmatic threshold. If lead migration causes the diaphragmatic stimulation threshold to decrease, then an LV pacing pulse initially set to avoid inadvertent stimulation of the diaphragm may nevertheless result in such stimulation. Likewise, if lead migration or other factors cause the LV capture threshold to increase, then an LV pacing pulse initially set to a pulse magnitude sufficient to depolarize the LV may fail to do so. Still further, thresholds may change once the patient becomes ambulatory following device implant.
State-of-the-art multi-electrode LV leads for use with CRT (such as St. Jude Medical's quadripolar Quartet™ lead) allow for “electronic repositioning”, i.e. the lead provides a set of electrodes for implant at different locations along the LV that can be independently selected for use in delivering pacing pulses so as to help avoid diaphragmatic stimulation while ensuring LV capture. For example, if the most distal of the LV electrodes (i.e. the LV tip electrode) is initially used for delivering pacing pulses to the LV but lead migration eventually causes those pulses to also trigger diaphragmatic stimulation, then another one of the electrodes of the LV lead (at a more proximal location) can instead be selected for delivering LV stimulation. In general, any combination of the LV electrodes may be selected—in conjunction with right ventricular (RV) lead electrodes or other electrodes—to define one or more pacing vectors for delivery of stimulation. In this manner, lead migration problems can be addressed through electronic repositioning (in combination with any needed adjustments to the pulse magnitude or other programmable pacing parameters) so as to deliver LV pacing above the LV capture threshold while avoiding diaphragmatic stimulation. Electronic repositioning can save implant time as well as reduce the need for post-operative lead re-intervention. In practice, a clinician uses an external programmer to control the implanted CRT device to perform various capture threshold tests using various combinations of pacing vectors to identify a suitable pacing vector to ensure LV capture without diaphragmatic stimulation.
Electronic repositioning is discussed, for example, U.S. Patent Application 2011/0213260 of Keel et at, entitled “CRT Lead Placement based on Optimal Branch Selection and Optimal Site Selection”; U.S. Patent Application 2011/0184274 entitled Rosenberg et al., entitled “Electrode Configurations for Leads or Catheters to Enhance Localization using a Localization System”; U.S. Patent Application 2011/0066203 of Rosenberg et al., entitled “Electrode and Lead Stability Indexes and Stability Maps based on Localization System Data” and U.S. Pat. No. 7,917,194 to Reed et al., entitled “Method and Apparatus for Detecting Pulmonary Edema.”
However, a quadripolar LV lead offers numerous programmable pacing/sensing vectors and so testing the capture thresholds and diaphragmatic stimulation thresholds for the entire set of programmable vectors can be complicated and time consuming. In particular, the workflow that a clinician typically must go through to perform and manage the various tests to identify suitable pacing vectors can be complex and time consuming. A multi-electrode lead with more electrodes would present an even greater number of vectors. A quicker, easier and more systematic method for testing and documenting suitable vector or vectors is desirable to facilitate lead positioning and vector selection and to simplify clinician workflow. It is to this end that aspects of the invention are generally directed.